The present invention relates generally to the field of power conversion systems. More particularly, embodiments of the present invention employ various architectures of power conversion systems and various methods to convert power. Still more particularly, embodiments of the present invention relate to power conversion systems for power generated by fuel cells.
Fuel cell systems are currently being used in a variety of power supply applications. If an application requires a particular voltage or current, fuel cells are combined into units called “stacks” in which the fuel cells are electrically connected in series to meet the requirements. A generalization of a fuel cell stack is the so-called fuel cell segment or column, which can contain one or more fuel cell stacks. In certain applications, many fuel cell segments may be required for higher power due to the limitation of current carrying capability of the fuel cells. For reliable operation, individual stack current can be controlled, to improve fuel utilization.
Fuel cells generate power that is converted in a fuel cell power conversion system, also known as a power conditioning system. A power conversion system is a system that alters the characteristics of power produced by a source in some way. For the case of fuel cells, which generate DC (direct current) power, this can mean the conversion of the DC power to different voltage and/or current levels, the conversion to AC (alternating current) power with a particular RMS (root mean squared) voltage, the generation of three-phase AC power, or all of the above. Typically, a change in the voltage level of a DC source can be accomplished using a DC/DC (direct current/direct current) converter, whereas the change from DC to AC is accomplished using a DC/AC (direct current/alternating current) converter or inverter.
The expected increase in fuel cell use in the future, in terms of both volume and number of applications, requires that the design and construction of fuel cell power systems be made as efficient as possible. To facilitate the design and manufacturing of fuel cell power control systems, it is advantageous to allow design flexibility while minimizing the number of components required to produce such an architecture.
In particular, it is of interest in power generation systems using fuel cells to reduce the effect of ripple currents through the fuel cells. Ripple currents are AC (alternating current) components of the total current function of the fuel cell. Ripple currents can be produce by a variety of components in a fuel cell system. Ripple currents can cause inefficient power generation by fuel cells and can damage a fuel cell. Thus, there is a need to reduce the effect of ripple currents in fuel cell systems.